The proposed research has three purposes: (1) To estimate the size of the undocumented population of Mexican origin in the SMSA's (and in the state-level residual nonmetropolitan areas) of the U.S. in 1980; (2) To estimate the effects of the characteristics of metropolitan labor markets on the number of undocumented persons (especially males) of Mexican origin counted in the 1980 Census in those labor markets; and (3) To estimate directly the effect of undocumented workers on the employment and earnings of the legally resident Mexican American and (where appropriate) other racial/ethnic male populations in such labor markets. The results of the second phase of the analysis, together with the estimates of the counted undocumented population, will constitute the basis for specifying an econometric model of labor demand that can be used to estimate the effects on the earnings of legally resident Mexican American and other workers. Our study will utilize data from the 1970 and 1980 U.S. Censuses, Public Use Sample Microfiles and the 1979 Alien Address Microfile from the INS to obtain area-specific estimates of the undocumented population.